Parameter input rotary-freq

[jmercat]

This allows to change the rotary positional embedding frequency parameter.
This is useful given the more recent approaches:
LLaMA 1&2 used 10000 which is the default value here.
LLaMA 3 uses 500000, Mistral uses 1000000
LLaMA long context extension works usually increase from 10000 to 100000.

[jmercat]

To test my changes I ran training with a small model and put a breakpoint where the parameter is used in rotary.py. I set a different value both in command line or in the json file and it was correctly passed on. Training was successful and tests passed. (except one in grad_accum and one in tokenize but not due to this PR, just access right issues).